There are numerous assemblies and methods for making and using integrated circuit heat cooling devices in the prior art. For example, the classic technique for removing excess heat from an integrated circuit or other electronic device involves attaching a heat sink to the integrated circuit or other electronic device. This heat sink typically includes a plurality of extruded, planar fins whose large surface area efficiently dissipates heat into the surrounding air or into a coolant circulating inside the fins.
Typically, heat transfer between the hot surface of a heat generating device and the surrounding air is the least efficient means of dissipating excess heat. Use of a heat sink significantly improves this heat transfer by increasing the surface area in contact with the cooling ambient (e.g. air or liquid). As a result, the device's operating temperature is lowered, and its performance reliability and life expectancy are increased.
A thermally conductive path is formed by attaching the heat sink to a surface of the electronic device to be cooled. Typically, this path includes a thermal interface material sandwiched between a contact surface of the heat sink and a contact surface of the electronic device. Depending on the embodiment, the thermal interface material may be malleable, electrically conductive, or electrically isolating. Exemplary electrically conductive thermal interfaces include: thermal greases filled with metallic particles, thermal adhesives, and thin films. Exemplary electrically isolating thermal interfaces include: gap fillers, double sided tapes, and pads. Thermal greases include Sil-Free™, a metal-oxide filled, silicone-free, synthetic grease manufactured by Aavid Thermalloy of Concord, N.H. Sil-Free™ is specially designed for bonding heat sinks to semi-conductor cases, and will not dry out, harden, melt, or run even after long term continuous exposure to temperatures up to 200 degrees Celsius.
Other types of thermal interfaces include silicone-based thermal greases and phase-changing materials. One type of phase-changing material is a solid, silicone-free, paraffin-based thermal compound manufactured by Aavid Thermalloy of Concord, N.H. that changes phase at approximately 60 degrees Celsius, with a concurrent volumetric expansion that fills gaps between the mating surfaces.
Thermally conductive adhesives offer excellent heat transfer and high voltage isolation. Typically manufactured as epoxies that offer low shrinkage and coefficients of thermal expansion comparable to copper or aluminum, thermally conductive adhesives bond readily to metals, glass, ceramics, and most plastics.
Thin films are cost-effective alternatives to thermally conductive grease compounds. Thin films may be applied with commercial hot-stamping equipment to the surfaces of heat producing devices; and such films yield excellent thermal performance while obviating the need for adhesives.
Gap-fillers are “super-soft”, low durometer materials designed to fill gaps between hot components and their heat sinks. The flexible elastic nature of gap fillers allows them to blanket uneven surfaces, and to conduct heat away from individual components, or an entire printed circuit board, into metal covers, frames, or spreader plates.
Double-sided tapes may be used to adhere the heat sink to the hot component. They are easily applied, require no curing time, can be electrically conductive or isolating, and require no mechanical support to provide thermal or by physical contact between the heat conductive device and the heat sink.
Thermal interface pads are typically thicker than double sided tapes, but can be provided without adhesive if removal of the pad is necessary. Although pads can be either electrically conductive or insulating, performance of the interface depends on maintenance of correct, constant mounting pressure applied to the pads.
Based on the above discussion, it will be appreciated that a plurality of heat exchangers may be attached to one or more surfaces of an electronic device using mounting clips, adhesives, or extruded pins. It will also be appreciated that the cooling fins, and heat exchangers themselves, may take a variety of configurations. For example, the surfaces of the cooling fins may be flat or dimpled, and the fins themselves may be bonded or folded. Bonded fins tend to dissipate more heat than conventional aluminum heat sinks with the same footprint, and manufacturing techniques permit increased fin ratios of 30:1 and higher. Increasing the number of fins increases the surface area exposed to cooling air, and greater exposed surface area means more heat transferred away from the heat conducting device. Folded fin designs offer maximum cooling surface in minimum volume, and may be manufactured of such materials as aluminum or copper. Liquid-cooled cold plates can provide cooling where aircooling techniques are impractical or inadequate. Liquid-cooled cold plates dissipate more heat with less flow volume of cooling ambient (as compared to air), maintain better temperature consistency, and create less acoustic noise than air-cooled heat exchangers.
As shown in FIG. 1, a conventional heat sink 100 includes a base material 101 having a contact surface 102 and a finned surface 103. The finned surface 103 is formed of a plurality of planar sections (or fins) 104 that are vertically disposed such that their planar surfaces parallel each other. Typically, adjacent fins are separated by an air channel 105. The air channel 105 develops airflow through the heat sink fins 104. The airflow cools an electronic device attached to the contact surface 102 of the heat sink 100 by dissipating the heat conducted through heat sink 100 and accumulated in fins 104. The base material 101 and fins 104 may be manufactured of any suitable heat-conductive material, such as aluminum.
FIG. 2 shows one example of a prior art liquid-cooled heat exchanger 200. As shown in FIG. 2, the base material 201 and fins 204 may be hollow, or may contain a hollow tube (or tubes) (not shown). A liquid coolant (or fluid) 206, such as water, may be introduced into the hollow base material 201 and/or fins 204, and heated or cooled in order to affect or control the temperature of the electronic device 207 attached to the heat exchanger 200. Alternatively, the liquid coolant 206 may be introduced into the hollow tube (not shown) under pressure, and heated or cooled in order to affect or control the temperature of the electronic device 207 attached to the heat exchanger 200.
In certain applications, however, such as portable computers, factors such as size, weight, and cost are important. However, adding conventional heat sinks to the computer's internal electrical components can increase its size, weight, and cost, thereby making the computer less profitable and less competitive in the marketplace. A significant drawback associated with conventional heat exchangers is the high cost of ensuring the near-perfect co-planarity of the heat exchanger and electrical component mating surfaces. Co-planarity of mating surfaces is important because the more co-planar the two surfaces are, the more efficient the heat transfer. However, it is difficult to manufacture co-planar mating surfaces smooth enough to produce an effective thermal contact.
Because of manufacturing limitations, several techniques and assemblies have been developed that can be used to form an efficient thermal contact between substantially co-planar mating surfaces. For example, a device manufactured by IBM of White Plains, N.Y., uses pistons which drive the heat exchanger (or cylindrical portions of the heat exchanger) down onto a printed circuit board or other electronic device. Although the pressure exerted by the expanding pistons ensures an efficient thermal contact with the heat producing device, such assemblies are expensive to manufacture, expensive to maintain, heavy, and rarely solve any co-planarity issues that might exist when making physical contact with multiple integrated circuits mounted on the heat producing device (e.g. printed circuit board).
Thus, it is desirable to provide an improved, non-conventional cooling device assembly and techniques which may take advantage of a hollow, resilient material having spring-like characteristics that provides a spring-like force when compressed against and in contact with a surface of an integrated circuit or other heat producing device.